Why did President Hadi sign off on the Jeddah agreement?My first...

Why did President Hadi sign off on the Jeddah agreement?

My first thought is the UAE withdrawing and stating its reason for such action openly. The developing background to this decision must have come over many months with talk between the two princes: MBS and MBZ of the coalition.

Whatever said, the UAE decision hurt and in all probability the Saudi went to plan B and worked on President Hadi. IMO, plan B's simple reasoning follows: the houthi fight is really a small proxy fight against Iran. Since the Houthi are still standing after 3 plus years and only the South STC have taken land of the Houthi if the Saudi pull out of the legitimate coalition forces there are cost benefits that should lead to other avenues for the Saudi's. Plan B's aim could be to just give the Southern STC more of a lead in the war. And they get that only if President Hadi will relent and let them in. To do that the Saudi need to convince Hadi that the UAE and Saudi's agree the war is not working and a withdraw program is on the way. The problem for President Hadi is what is left is his disaster: If the coalition leave Yemen, Houthi control North STC control south and he - not having a country, will stay in Riyadh. Nothing changes except Marib, the central depository for Coalition troops will not be able defend itself and the Houthi will probably overrun it. Getting oil to pipe to Ras Issa, north of Hodeiduh. Ouch!

Hadi has money and the Moslem Brotherhood will do deals where they are subordinate to the Houthi.
Meanwhile nothing will stop the STC going forward.

So if this ultimatum was given to President Hadi, I do not blame him countering with a request for immunity which was reported in twitter exchanges. It seems he got what he wanted.